Sulfur and sulfur containing compounds, e.g., H.sub.2 S, mercaptans, organic sulfides and disulfides, etc. are present in crude oil and remain to various degrees in the products obtained from the refining of these crude oils. For example, kerosine and gasoline can contain appreciable amounts of mercaptans which give these products an objectionable odor. One common way to make these products less malodorous is to convert the mercaptans to disulfides. This is known as sweetening. Although sweetening eliminates the mercaptans, it does not remove the sulfur compounds. As stricter pollution control regulations are passed, it is becoming necessary to actually remove the sulfur compounds and not just convert them to less malodorous compounds.
Sulfuric acid or sulfur dioxide is also used as a catalyst in various hydrocarbon conversion processes. However, in some cases sulfur compounds are formed as byproducts. For example, in the oxidative conversion of cumene to phenol and acetone, alphamethylstyrene is produced as a byproduct along with sulfur compounds such as ethyl mercaptan, dimethyl sulfide, diethyl disulfide and carbon disulfide. Sulfur free alphamethylstyrene is a saleable product and thus it is important to remove all the sulfur compounds from the alpha-methylstyrene. One way to remove these sulfur compounds is to use a nickel/clay mixture. However, this also polymerizes the alpha-methylstyrene to poly alpha-methylstyrene. Therefore, there is a need for a process to remove these sulfur compounds without polymerizing the alpha-methylstyrene.
Applicants have developed a process which removes the sulfur compounds without polymerizing the alpha-methylstyrene. This process involves contacting the alphamethylstyrene with an adsorbent which is a solid solution of metal oxides. The solid solution has the formula M.sub.a (II)M.sub.b (III)O.sub.(a+b) (OH).sub.b where M(II) is at least one metal having a +2 oxidation state, selected from the group consisting of magnesium, nickel, zinc, copper, iron, cobalt, calcium and mixtures thereof and M(III) is at least one metal having a +3 oxidation state and is selected from the group consisting of aluminum, chromium, gallium, scandium, iron, lanthanum, cerium, yttrium, boron and mixtures thereof and the ratio of a:b is greater than 1 to about 15. A preferred solid solution is a nickel oxide/magnesium oxide/aluminum oxide solid solution. The solid solution adsorbs the sulfur compounds without polymerizing the alpha-methylstyrene.
These metal oxide solid solutions are also capable of removing mercaptans from kerosine or hydrogen sulfide from hydrocarbon streams such as toluene. In both of these cases, the sulfur compounds are removed without affecting the desired product, i.e., no reaction takes place between the solid solution (adsorbent) and the feedstream.
The prior art has concerned itself with removing sulfur compounds from gas mixtures. For example, U.S. Pat. No. 5,114,898 discloses that layered double hydroxides (LDH) having the formula EQU (M.sub.1-x.sup.II M.sub.x.sup.III (OH).sub.2)(A.sup.n-).sub.x/n.pH.sub.2 O
where M.sup.II is a divalent metal cation, M.sup.III is a trivalent metal cation and A is an interlayer anion of charge n.sup.-. The process involves contacting the flue gas with the LDH at temperatures of 500.degree. to 1000.degree. C., in order to adsorb the SO.sub.x onto the LDH. It should be pointed out that LDHs are precursors of solid solutions. That is, a solid solution is usually prepared from an LDH by heating the LDH at a temperature of about 300.degree. to about 700.degree. C.
In contrast, applicants use a solid solution of metal oxides to adsorb sulfur compounds from a liquid organic feedstream. The contacting is carried out at room temperature or slightly above room temperature. There is no hint in the '898 reference that a solid solution derived from an LDH could adsorb sulfur compounds from a liquid organic feedstream. Thus, applicants are the first to have developed such a process.